 (defprotocol SpatialRelations
   "Defines functions for determining relations between different spatial areas."
 
+  (coordinate-system
+    [shape]
+    "Returns the coordinate system of a shape if it has one. Points do not occupy
+    a set coordinate system.")
+
   (mbr [shape] "Returns the minimum bounding rectangle of the shape")
 
   (contains-north-pole? [shape] "Returns true if the shape contains the north pole")

  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  cmr.spatial.geodetic_ring.GeodeticRing

  (mbr
    [ring]
    (:mbr ring))


  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  cmr.spatial.mbr.Mbr

  (coordinate-system
    [_]
    :cartesian)

  (mbr [br] br)

